Wave actuator

ABSTRACT

A two dimensional structure such as a disk or belt is shaped or distorted to form a buckling wave. At least one contact touches the wave, two contacts squeezing the wave between them providing a firmer connection. The wave is propagated along the structure by any of a variety of means including magnets or piezo actuators. This movement of the wave moves the contacts relative to the two dimensional structure, providing a high leverage ratio.

TECHNICAL FIELD

Actuators.

BACKGROUND

The inventor has previously disclosed actuators using flexible splines,for example in PCT application published under the number WO2015/168793. A new actuator is disclosed.

SUMMARY

There is a disclosed a device and method for making a device, that usesa propagating wave to actuate an output member.

In an embodiment, there is disclosed a wave actuator comprising a twodimensional structure having at least a portion pre-stressed incompression in a first direction of the two dimensional structure toform a wave shape having waves along the first direction; an outputarranged in contact with the waves of the wave shape, the output and thetwo-dimensional structure movably arranged in relation to one another;and a wave propagator arranged to propagate the waves along the firstdirection to move the output relative to the two dimensional structure.

In an embodiment, there is disclosed a method of making a wave actuator,the method comprising providing a disk with a circumference in aninitial state, loading the disk in tension across the disk andcompression along the circumference to cause the disk to buckle and forma wave shape with waves: and constraining the disk between outputmembers with the output members contacting the disk at one or more waveapexes such that force can be transferred from the disk to the outputmembers when a wave is propagated along the disk.

In an embodiment, there is disclosed a torque transfer device comprisinga wave disk, the wave disk having an axis, the wave disk being preloadedin tension radially and in compression along the outer circumferencesuch that a circumferential buckling effect is produced to generate anaxial wave with two or more wave crests and troughs; one or more outputcontact rings attached coaxially to a rotating output member and axiallypreloaded against the axial wave apexes; and a propagating means tocircumferentially propagate the wave to impart rotation and torque fromthe wave disk to the output members.

In various embodiments, there may be included one or more of: the outputcomprises a first output member and a second output member, the waveshape being constrained between the first output member and the secondoutput member; the first output member is rigidly connected to thesecond output member; the wave shape comprises a first contact surfacethat contacts the first output member and a second contact surface thatcontacts the second output member, one of the contact surfaces beingoffset in a direction generally perpendicular to the two-dimensionalstructure to cause the wave actuator to differentially move the firstoutput member and the second output member; a slot in the one of thecontact surfaces that is offset in the direction generally perpendicularto the two-dimensional structure; the wave propagator comprises piezoactuators or electromagnets, in various configurations, the output is infriction or geared contact with the waves of the wave shape; the diskhas axially elongated teeth; a reference member, the wave shape beingconstrained between the output and the reference member; groovesextending generally in the first direction in each of the disk and theoutput; the tensioning member comprises generally radial spokes intension; the two dimensional structure is a belt.

These and other aspects of the device and method are set out in theclaims.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments will now be described with reference to the figures, inwhich like reference characters denote like elements, by way of example,and in which:

FIG. 1 is an axial view of an embodiment of a wave disk;

FIG. 2 is a detail view of a radial slot between spokes of the wave diskof FIG. 1;

FIG. 3 is a perspective section view of a device including the wave diskof FIG. 1;

FIG. 4 is a close-up section view of the wave disk of FIG. 1;

FIGS. 5A-5C are side, 45 degree angle, and top views respectively of thewave disk of FIG. 1 showing the wave shape;

FIGS. 6A-6C are axial, perspective, and close up radial viewsrespectively of an embodiment of a wave disk having lobed output rings;

FIG. 7 is a cutaway perspective view of an embodiment of a wave diskhaving permanent magnets;

FIG. 8 is a cutaway perspective view of the embodiment of FIG. 7 alsoshowing electromagnets arranged to move the permanent magnets;

FIG. 9 is a cutaway perspective view of a wave disk havingelectromagnets;

FIG. 10 is a cutaway perspective view of a wave disk device with ridgesand matching grooves on the contacting surfaces of the wave disk and theoutput members;

FIG. 11 is a schematic illustration showing an axial view of anembodiment of a wave disk, not yet pre-loaded to obtain a wave shape;

FIG. 12 is a schematic illustration showing a radial view of theembodiment of FIG. 11;

FIG. 13 is a schematic illustration showing a perspective view of theembodiment of FIG. 11;

FIG. 14 is a schematic illustration showing a perspective view of theembodiment of FIG. 11 now preloaded to obtain a wave shape;

FIG. 15 is a perspective section view of a disk positioned for the outerring to be compressed and circumferentially elongated between twomandrels;

FIG. 16 is a close-up section view of the outer ring of the disk of FIG.15 undergoing compression between the two mandrels;

FIG. 17 is a cutaway view of the disk of FIG. 16, post compression,being exposed to an axial preload to obtain a three wave shape;

FIG. 18 shows the disk of FIG. 17 with four waves;

FIG. 19 shows the disk of FIG. 17 with five waves;

FIG. 20 shows the disk of FIG. 17 with six waves;

FIG. 21 shows the disk of FIG. 17 with seven waves;

FIG. 22 shows the disk of FIG. 17 with eight waves;

FIG. 23 shows the disk of FIG. 17 with nine waves;

FIG. 24 shows the disk of FIG. 17 with ten waves;

FIG. 25 shows the disk of FIG. 17 with eleven waves and positionedbetween axial load members;

FIG. 26 is a section view of the disk and load members of FIG. 25;

FIG. 27 is an axial view of an embodiment of a disk having cut-outs;

FIG. 28 is a radial view of the embodiment of FIG. 27;

FIG. 29 is another radial view of the embodiment of FIG. 27, at an anglemore clearly showing the disk with no preload showing the at-rest twowave shape;

FIG. 30 is a section perspective view of the embodiment of FIG. 27;

FIG. 31 is a section perspective view of the embodiment of FIG. 27 withpiezo strips added to propagate the wave;

FIG. 32 is a cutaway perspective view of the embodiment of FIG. 31showing the maximum elastic bending deflection of the spokes;

FIG. 33 is a graph showing the change in voltage over time at differentpoles of the device of FIG. 31 during commutation;

FIG. 34 is a radial view of the device of FIG. 31 showing the positionsof the poles at the time indicated by the dashed line in FIG. 33;

FIG. 35 is a simplified schematic diagram showing an embodiment of acontrol system to propagate waves on a wave disk;

FIG. 36 is an axial view of an embodiment of a wave disk using injectionmolding with lower CTE inserts to achieve a wave shape when the diskcools before removal from mold;

FIG. 37 is a close-up perspective view of the outer diameter ring of theembodiment of FIG. 36 with hidden lines visible to show the lower CTEinserts;

FIG. 38 is an axial view of another injection molded embodimentcontaining a continuous ring insert with a lower CTE than the injectionmolded ring;

FIG. 39 is a close-up perspective section view of the embodiment of FIG.38 showing the insert;

FIG. 40 is a perspective section view of an embodiment of a wave diskwith an asymmetrical outer diameter ring allowing torque transferbetween different sides of the housing;

FIG. 41 is a close-up section view of the embodiment of FIG. 40;

FIG. 42 is a perspective section view of an embodiment of anasymmetrical outer diameter ring having slots to allow circumferentialexpansion and contraction during wave propagation;

FIG. 43 is a perspective section view of the embodiment of FIG. 42deployed in the split housing of FIG. 40;

FIGS. 44-46 are an axial, close-up axial and perspective viewrespectively of a lobed configuration of wave disk and output rings;

FIG. 47 is a perspective section view of an embodiment with permanentmagnets on one or both sides of the wave disk and an array ofelectromagnetic coils attached to a housing disk;

FIG. 48 is a perspective section view of a simplified partial assemblyexample of a three wave circumferentially buckled inner diameter ringdisk, in a housing;

FIG. 49 is a perspective section view of the disk of FIG. 48 without thehousing but buckled into a three wave shape as if axially preloaded bythe housing;

FIG. 50 is a schematic perspective section view of a linear actuatorusing the principles of the present disclosure;

FIG. 51 is a schematic perspective section view of the linear actuatorof FIG. 50 showing the wave plate only;

FIG. 52 is a partially assembled, partial perspective view of a waveplate having a stack of radially bending piezoelectric actuators usedfor commutation which apply an axial force on the wave disk;

FIG. 53 is a section view of the wave plate and piezo stack of FIG. 52;

FIG. 54 is a sectional schematic example showing how radially expandingor contracting actuators can expand or contract to produce an axial wavepropagation effect;

FIG. 55 is a perspective cutaway view of a schematic of a linear waveplate (or foil) with electroactive wave propagating elements adhered tothe surfaces of the wave foils;

FIG. 56 is an end view of the schematic of FIG. 55;

FIG. 57 is an end view of a linear actuator with the wave foils fixed tothe outer member;

FIG. 58 is a perspective cutaway view of the linear actuator of FIG. 57;

FIG. 59 is a section view of the linear actuator of FIG. 58;

FIG. 60 is a partial view of a schematic of a wave foil;

FIG. 61 is a partial view of the schematic of the wave foil of FIG. 60,showing the wave of the wave foil;

FIGS. 62A and 62B are respectively a top view and an end view of a 90degree arc foil;

FIG. 63 is a top view of a buckled 90 degree arc foil superimposed on anat-rest arc foil;

FIG. 64 is a perspective view of the superimposed foils of FIG. 63showing the wave shape;

FIG. 65 is a perspective view of an arc foil between two outputsurfaces;

FIG. 66 is a perspective view showing an arc foil at rest on the rightand bent on the left;

FIG. 67 is an axial view of a wave disk embodiment;

FIG. 68 is a detail view of a cutout along the centerline of a set ofopposing actuators of the wave disk of FIG. 67;

FIG. 69 is a perspective view of a simplified partial assembly of arotating non-contacting permanent magnet wave propagation configuration;

FIG. 70 is a perspective view of a spinning input member withnon-contacting permanent magnets and a contacting rolling wavepropagation member;

FIG. 71 is a radial view of partial assembly of a lobed wave disk andlobed output rings illustrating axially elongated disk lobes with lobeson one axial side of the wave disk being longer than the lobes on theopposite side to produce differential rotation of planar contactmembers;

FIG. 72 is a detail view of the partial assembly of FIG. 71;

FIGS. 73-75 show steps in a method of manufacture of a wave actuator;and

FIG. 76 shows a schematic of a roll forming manufacturing method.

DETAILED DESCRIPTION

Immaterial modifications may be made to the embodiments described herewithout departing from what is covered by the claims.

A wave actuator may comprise a two dimensional structure having at leasta portion pre-stressed in compression in a first direction of the twodimensional structure to form a wave shape having waves along the firstdirection, an output arranged in contact with the waves of the waveshape, the output and the two-dimensional structure movably arranged inrelation to one another, and a wave propagator arranged to propagate thewaves along the first direction to move the output relative to the twodimensional structure. The two dimensional structure may be, forexample, a disk or a belt. The two dimensional structure can besheet-like, but may have cut-outs and may also comprise spokes or otherlinear members. It may have a complicated structure including extensionsperpendicular to the generally two dimensional structure.

For a disk the circumferential compressive load is the result of anevenly distributed radially tensioned disk or spoke or flexure arrayetc. That is, a disk should have a rotationally symmetric radial loadingof the disk section radially inward from the ring.

The two dimensional structure need not be flat or planar; a benttwo-dimensional structure is still two dimensional. The output typicallyhas a two dimensional surface generally parallel to the two dimensionalstructure taken as a whole, but may not be parallel locally to the twodimensional structure due to the wave shape. Compression of the waveshape against the surface may in turn press the wave shape intoconformity with the surface locally where it contacts the surface. Wherethe two dimensional structure is a disk, typically the pre-stressing incompression is a circumferential pre-stressing in compression forcing acircumferential waves about the disk, the propagation of the waves andthe resulting movement of the output also being circumferential. Wherethe two dimensional structure is a belt, typically the compression isalong an edge of the belt to form a wave shape along the edge of thebelt, the propagation of the waves and the resulting movement of theoutput also being along the edge, thus typically along the length of thebelt for a consistent width belt with edges parallel to the length ofthe belt. An arc-shaped two dimensional structure can be considered tobe a curved belt. The pre-stressing in compression of a circumferentialportion of a disk can be accomplished, for example, by tensioningmembers acting to constrain the radial width of the circumferentialportion. The radial width can also be constrained by radial compressionfrom the outside, though this is a less typical embodiment. Thepre-stressing in compression for a belt can be accomplished, forexample, by constraining the length of the belt using a tensioningmember. The tensioning member can be, for example, offset from the edgeof the belt to avoid interfering with waves formed at the edge of thebelt. Typically the wave shape is constrained between two outputsurfaces for better traction.

The output surfaces can be rigidly connected to each other. The outputmay be fixed or the two dimensional structure may be fixed or neithermay be fixed. The output surfaces may be movable with respect to oneanother and the two dimensional structure configured to differentiallymove the output surfaces. Where one output surface is movable withrespect to another, one may act as a reference for the output of theother, the desired motion being the motion of the output relative to thereference. The configuration of the two dimensional structure todifferentially move the output surfaces may be accomplished for exampleby offsetting one side of the two dimensional structure at a portionthat contacts an output surface in a direction perpendicular to the twodimensional structure. In the case of a disk, this perpendicular offsetis an axial offset.

In an embodiment of wave actuator, the wave actuator includes a circularwave disk which is circumferentially pre-stressed in compression andradially constrained to prevent outward displacement of the disk outerdiameter (OD) and with a flexible member/s so as to generate an axialwave shape around the OD. This wave is, in one example, similar in shapeto a hyperbolic paraboloid, but unlike a more common hyperbolicparaboloid, it is not a rigid shape. Rather, when constructed accordingto the principles of this disclosure, a wave apex does not have a biasedangular position around the circumference and can be propagated in thecircumferential direction with minimal force and minimal mechanicalloss. The disk will always revert to a two wave (two peaks and twotroughs) shape when not axially loaded against the output disks. Onlywhen axial preload is applied to the two wave shape will it transitioninto a shape with greater than two waves. Axially loading disks or ringsor other output members are necessary for all wave numbers above two andthey are not necessarily shown in each drawing.

An exemplary embodiment of the device comprises one or more wave diskshaving the following features: a preferably but not necessarily axiallythicker ring section at or near the OD of the disk; a center axis withor without a through hole (for the purpose of clarity in thisdisclosure, the center axis area will use a through hole for mostembodiments and will be referred to as the inner diameter (ID)); a diskarea preferably but not necessarily axially thinner than the OD ringsection which is able to bend in one or both axial directions but notsubstantially in the circumferential direction as the wave ispropagated; the disk preferably has a means of centering the disk on therotational axis of the device such as but not limited to with abushing/s or bearing/s between the disk and an output member, or teethor lobes on the disk that mesh with teeth or lobes or meshingcircumferential grooves on the disk and on an output member such thatthe disk is constrained from movement in all radial directions; and theexemplary wave disk having one or more contact surfaces on one or moreaxially facing surfaces of a disk which transmit rotation and torquefrom the disk to a mating surface on an output member. This surfaceinterface can be, but is not limited to a traction interface, a gearedor lobed interface, a generally planar surface on the disk at thecontact position, a generally conical surface on the disk at the contactposition, a generally toroidal surface on the disk at the contactposition, or a ridged surface as shown in FIG. 10 with one or morecircumferentially aligned ridges 26 and/or grooves 28 that increase thecontact surface area and increase the surface contact pressure as aresult of a wedging effect between the disk and housing member ridges 26and grooves 28. This exemplary embodiment also has means of propagatingone or more wave apexes in either circumferential direction to changethe angular position of a contact between a disk and a housing memberincluding, but not limited to: electromagnets pulling directly on a softmetallic material attached to the disk (or the disk itself being made ofa soft magnetic material such as, but not limited to 4340 steel),electromagnets pulling on permanent magnets attached to any portion of adisk which moves in a direction when a wave is propagated, piezo ceramicmaterial pulling and/or pushing and/or causing elastic deformation ofany portion of a disk which moves in a direction when a wave ispropagated, thermal expansion and/or contraction of any portion of adisk which moves in a direction when a wave is propagated, hydraulicpressure acting on any portion of a disk which moves in a direction whena wave is propagated, aero dynamic forces and/or pressure of a gasacting on any portion of a disk which moves in a direction when a waveis propagate, electro-reactive materials acting on any portion of a diskwhich moves in a direction when a wave is propagated, or a wide range ofactuators or actuating materials or devices that can also be used topropagate a wave on a disk. Generally speaking, any point on a disk thatmoves in a direction when a wave is propagated can be used as anactuation point by exerting a force on that point with an actuatingmeans. The other attachment point for an actuator or actuator means canbe on the disk itself or on a housing member or on an output member.This exemplary embodiment also has one or more output members having apreferably circular contact section at a similar radial dimension of thedisk contact section facing toward and meshing with the disk so as totransmit torque form the disk to the output member. Two surfaces on theoutput members may be provided on either axial end of a disk and axiallyspaced to contact the disk on both axial sides of the disk. Axialspacing of the output members may be arranged to axially preload theapexes of the disk so the contact surfaces are always preloaded.Furthermore, more than one of the above disks may be sandwiched betweenmore than one set of output members to increase the torque capacity.

Some potential variations include: a disk can be used as a referencemember with both axial ends of said disk transmitting torque to axiallyinward facing surfaces on an output member that are fixed to each other.In this configuration, it is preferable for the disk to be symmetricalacross a plane that is perpendicular to the rotational axis. A disk canbe asymmetrical on either side of a plane that is perpendicular to therotational axis (such as, but not limited to, for example with a contactsurface of the ring being axially further from the disk material inwardfrom the OD ring) such that one contact surface on one axial end has adifferent disk-to-output member contact patch speed ratio than theopposing disk-to-output member contact patch speed ratio. In this case,each of the two output members may have a different speed ratio relativeto the disk as the disk wave propagates while said disk can be freefloating or attached to a different input or output. This configurationwould preferably use a bearing between opposing output members toprovide axial loading of the surfaces. More briefly described variationsare: multiple stages used in series or parallel; use of the device as amotor or generator, use as a speed increaser or decreaser, direct driveof the wave disk with actuators as described above, drive of the wavedisk with a rotary input such as to generate electricity or other modeof power; and a variable ratio output may be achievable by varying theaxial displacement of the disk relative to one or both output members orthe output member axial spacing.

Non-Limiting Example of One of Many Ways to Construct the Present Device

An exemplary embodiment of wave disk 1 has an array of radialblade/spokes 3 as shown in FIG. 1. The disk 1 can be a number ofdifferent materials or different sizes, but in this non-limitingexample, the wave disk is 8″ in diameter and is made of titanium. Theinner diameter (ID) hub 20 is radially slotted to allow inward radialdisplacement of the spokes without interference between the spokes. Asshown in FIG. 2, with the spokes in the drawn-in position, the generallyradial slots 4 between the spokes allow the spokes to be drawn radiallyinward a desired distance without interference with each other.

As shown in FIG. 3, preferably curved or conical surfaces 8 on outputmembers 9 are drawn axially inward with, for example, bolts (not shown)to rigidly connect the two output members. The conical surfaces 8axially compress the wave disk OD ring 2 generating preferably axiallypreloaded contact between the wave disk OD ring 2 and the output contactsurfaces 8. Radial displacement can be accomplished in a number of ways.In this exemplary embodiment, as shown in FIG. 4, two preferably conicalsleeves 5 are axially drawn radially inward (using bolts or threads orother means—not shown in images) around conical sleeves 7 on the ID huband generate a resulting radially inward force and displacement ofbetween 0.002″ and 0.020″ (although higher or lower displacements maywork for some geometries and applications). This pulls the ID of thespokes inward and creates inward radial tension on the spokes. In thisschematic image, the tapered surfaces 7 of the disk are showninterfering. The outer diameter (OD) ring section 2 is notcircumferentially interrupted like the spokes and is therefore resistantto compression in the circumferential direction. It is also preferablythicker than the spokes 3. The inward tension on the spokes results in acircumferential compression loading of the OD ring causing it to buckleinto a circumferential wave with an axial magnitude of between 0.002″and 0.2″ (although greater or smaller wave magnitudes are possible andmay be useful for some applications). The resulting wave shape, when notaxially preloaded against the output members, is similar to a hyperbolicparaboloid with two wave crests and two wave troughs as shown in FIGS.5A-5C.

As shown in FIG. 3, a pair of preferably symmetrical output surfaces 8are fixed to an output housing member 9 so they rotate together as onepiece about the center axis of the actuator. These two surfaces aredrawn together in the axial direction by bolts or other means (not shownin images) with the wave disk sandwiched in-between them. If the wavedisk has axial lobes or teeth 22 (as shown in FIGS. 6A-6C) then therequired preload may be just high enough to keep the lobes engaged undermaximum torque. FIGS. 6A-6C show an example of a lobed surface withelongated lobes that engage with lobed output rings. The teeth on oneside of the disk may be at a different radial position from teeth on theother side. If the contact surfaces are designed for traction torquetransfer, the preload force are preferably higher than is necessary withgears or lobes. In this exemplary embodiment, two waves result from thecircumferential buckling. Up to a critical axial preload, the wave diskwill maintain two wave peaks and two wave troughs. With additional axialpreload, the wave disk will find a lower energy shape with three waves.With still higher axial preload the wave disk will find a lower energyshape with four lobes.

Additional waves will continue to form with additional preload and/oraxial displacement of the output members. The advantages of additionalwaves include smaller airgaps between wave disk and electromagnets ifelectromagnetically driven and increased total contact surface area asaxial preload increases.

The wave disk is preferably held coaxially to the output members by alow friction bearing. A flange for attachment to the fixed member of theactuated assembly (such as, but not limited to a robot base as onenon-limiting example) is included in the wave disk ID assemblyconstruction. A flange for attachment of the output member (such as, butnot limited to a robot arm) is included in the geometry of the outputmember.

As shown in FIG. 8 and FIG. 9, an array of electro magnets 12 ispreferably attached to disks 24 that are fixed to the ID hub of the wavedisk. They can also be attached to the output members. Theelectromagnets can be used on one or both sides of the disk but only oneside is shown here. These electromagnets exert a magnetic force directlyon the wave disk (embodiment not shown) or on permanent magnets 10imbedded in the disk or attached to the disk, or held to the disk with aflexible ring 11 (preferably but not necessarily made of titanium) asshown in FIG. 7. Commutating the EM coils 13 of the electromagnets drawsand/or repels the permanent magnets toward or away from the coils in theaxial direction and in so doing, propagate the wave. As the wavepropagates, the difference between the circumferential length of thedisk OD ring contact surface and the output contact circle defines thereduction ratio between the wave orbit and the output rotation. Ratiosof between 100:1 and up to 1000:1 are believed possible with greater andlesser ratios possible under certain conditions with specific materialsand geometry. The permanent magnets can be neodymium or other types ofmagnets. The titanium disk is beneficial in this configuration becauseit is highly flexible and resists the development of eddy currents. Theflexible coupling ring 11 could be made of many different materials.Titanium is considered to be a preferable material. The ring couplingmay be attached to the disk with fasteners such as bolts (not shownhere) connected for example to the spokes.

The device may have multiple wave disks, and need not have a throughhole.

Forged Plastic Disk (Non-Limiting Example)

Another exemplary embodiment uses a disk made of polycarbonate or otherpolymer with high strength, low creep modulus, and ability to retain ahigh percentage of its strength after plastic deformation, which isinitially manufactured as a rotationally symmetric disk shape with arotationally uninterrupted hub, a spoke array which is circumferentiallyinterrupted, and preferably axially thicker OD ring section that is notcircumferentially interrupted. The OD ring is then axially compressedbetween two dies beyond its compression strength limit. The plasticdeformation of the OD ring elongates the ring in the circumferentialdirection. This produces a circumferential compression (as a result ofthe spokes resisting radially outward movement of the now larger ODring, which then results in a circumferential wave deformation (withinthe elastic limit of the disk) when the die force is removed due tocircumferential buckling.

As with other embodiments in this disclosure, this wave can then becommutated by any number of actuation means such as with electro magnetsor piezo actuators or any of the types of actuators described in thisdisclosure. Piezo actuators may be arranged radially within the disk,for example along the axial surface of the spokes or disk and/orcircumferentially and/or at an angle between these two extremes. Radialpiezoelectric transducers will propagate a circumferential wave. Thereis a distinct advantage to radial piezoelectric transducers (“piezos”)in that the radial deflection near the ID is near zero. This providesthe opportunity to use piezos with very small deflection (which ischaracteristic of the strongest piezo material). The bending deflectionof the radial spokes increases radially outwardly. This also providesthe opportunity to use thicker piezo (or other electro reactive ormagnetostrictive, etc.) materials toward the ID for greater force inareas of lower deflection where the thicker material doesn't need tobend as much.

This design is not limited to plastic and can also be used with, forexample, metal; see FIGS. 15-26 and the corresponding description.

Injection Molded with Magnetic OD Ring (Non-Limiting Example)

Another exemplary embodiment uses a thermoplastic disk (although manyother materials which contract when cooled may be used) which isinjection molded (for example) in a rotationally symmetric disk shape(with no wave shape). It has a rotationally uninterrupted hub and mayhave a spoke array which is circumferentially interrupted, or it mayhave a rotationally uninterrupted disk shape, and preferably axiallythicker OD ring section that is not circumferentially interrupted. Asolid metal ring such as, but not limited to a steel ring having ahigher compression strength and a lower coefficient of thermalexpansion, is placed in the mold before the plastic is injected and heldwith spacers so it is completely encased in plastic when the mold isfilled. The plastic is preferably cooled to room temperature while themold is closed. When the mold is opened, the contraction of the plasticwill generate a radially inward force on the OD ring. The lesscompressible OD ring insert will, as a result, be loaded incircumferential compression and, with adequate contraction of the disk,be caused to buckle in the circumferential direction. The resultingcircumferential wave creation (within the elastic limit of the plasticdisk and steel or other OD ring material insert) can then be axiallycompressed between two output member contact faces. Propagating the wavewill transmit torque from the wave disk to the output member/s. Furtherdescription can be found in relation to FIGS. 36-39.

As with other embodiments in this disclosure, this wave can then becommutated by any number of actuation means such as with electro magnetsor piezo actuators or any of the types of actuators described in thisdisclosure.

For the above non-limiting examples, and for the many other ways thisdevice can be constructed according to the basic principles of thisdisclosure, the circumferential compression of the preferably, but notnecessarily axially thicker OD ring of the disk can be accomplished in anumber of ways including but not limited to the following: first,tensioning the area of the disk inward from the OD ring. This can bedone a number of ways including, but not limited to: radially tensionedradial spokes or blades, radially tensioned filaments such as but notlimited to cables or wires or belts or chains that connect an OD ring toand ID ring in a generally radial filament alignment, thermallyshrinking the ID of the disk, or mechanically shrinking the ID of thedisk such as, but not limited to using a tapered ring which elasticallyand/or plastically deforms the disk ID radially inwards. Second, axiallycompressing the OD ring section such as but not limited to by: dropforging the OD ring in the axial direction to cause plastic deformationof the OD ring, forging the OD ring in the axial direction to causeplastic deformation of the OD ring, roll forming the OD ring in thecircumferential direction to cause plastic deformation of the OD ring,or forging or drop forging or rolling the OD ring and areas radiallyinward from the OD ring, preferably with progressively less axialplastic deformation of the inward areas closer to the ID to create aprogressively more circumferential compression of the disk toward theOD. Third, imbedding a ring of higher compression stiffness materialnear the OD of the disk that resists compression of the disk in thecircumferential direction and creating radial tension on the lowerstiffness material such as, but not limited to by injection molding aring of material into the OD area of a thermoplastic disk with a highenough molding temperature and high enough thermal expansion coefficientthat when cooled, the contracting thermoplastic (or other suitablematerial) draws the OD of the disk inward. The circumferentially stifferring material resists circumferential compression and the OD of the diskfinds a lower energy shape similar to a hyperbolic paraboloid. Or, byusing a thermoplastic or other material that shrinks when cooled or asit sets (if a thermoset material with a high shrinkage rate), it ispreferable to let the disk cool completely before demolding so the diskdoes not bias to a particular wave location. The circumferentially lesscompressible ring can be a segmented array of materials such as, but notlimited to an array of permanent magnets that can also be used foractuation.

Additional Variations

Variations include more than two positive and negative waves per disksuch as if the disk is axially compressed beyond the distance where thelowest energy shape causes the disk to maintain a two wave shape. Inthis case the disk will find a lower energy shape with a greater numberof waves around its circumference. Specifically, as the axial distancebetween the output contact faces is reduced, the wave disk willtransition from two waves (two apexes in one axial direction and twowave apexes in the opposite axial direction, to three waves and then, atgreater displacement, four waves and then five waves and so on. This isconsidered to be a beneficial effect in that greater axial compressionresults in the following complementary effects (described here in theexample of three waves as compared to 2 waves).

With three waves, the axial displacement of the rotor is reduced whichreduces the maximum airgap between the disk and an electromagnetactuator array. This increases the magnetic force available to propagatethe wave. With three waves compared to two waves, an electromagnetarray, or other actuation method can be acting on three areas instead oftwo. With three waves instead of two, the elastic deflection of the diskwill be reduced making it better suited to actuation with high force butlow displacement actuation materials such as piezo ceramics. With threewaves instead of two, it is believed possible to reduce the contactpressure for a given total axial load, which may allow the use of lowerhardness materials for traction interfaces between the wave disk andoutput members. This may allow the use of resilient materials such as,but not limited to high friction coefficient rubber or polyurethane orother polymers. Increasing the number of waves for a given total preloadforce, more evenly distributes the contact forces of the wave disk onthe output members. This reduces the required stiffness of these partsallow for lower mass.

Also shown in FIGS. 71 and 72 is an example of a lobed surface withelongated lobes that splay apart before engagement to engagement withlobed output rings with reduced sliding contact. In an exemplaryembodiment of the device the smooth surfaces of the outer region of awave disc contacts axisymmetric smooth surfaces, referred to as plates,on both sides at equal distances from the center plane of the wave disc.The two plates are connected rotationally. When viewed along its axis ofrotation the wave disc is generally circular in shape and may have ahole through its center. When there is a hole through the center, itsdiameter is referred to as the ID. The wave disc is made by reducing theID of a flat disc component in order to reduce the mean radius of thecontinuous ring of material around its periphery. The distance along therim of the wave disc is then greater than the circumference of a circleof the projected radius and, when unrestrained, this excess materialnaturally deforms the wave disc into a shape similar to that of ahyperbolic paraboloid, with 2 crests in one axial direction from itscentral point and 2 crests in the other axial direction. The waves ofthis free shape have no preferential circumferential position, and sothey can be displaced, as a group, to a new position by applying minimalaxial (or somewhat axial or perpendicular) force at any surface notlying on a plane normal to the axis of symmetry. When compressed between2 plates the initial contact occurs at 2 crests on each side, but as thedistance between the plates reduces the quantity of waves automaticallyincreases incrementally at discrete positions. Because the deformedshape of the wave disc can be displaced circumferentially withoutsliding, very little force is required to move the deformation around.The developed length of the outer portion of the wave disc contactingthe 2 plates is longer than the developed length of the correspondingcontact region on the plates, therefore every time the set of wavesmakes a full rotation relative to the outer plates the wave disc makesmuch less than one rotation. Electromagnets mounted on carrier platesthat are connected to the inner portion of the wave disc sequentiallyattract and repel, in a generally axial direction, permanent magnetsmounted around the wave disc to force the deformation to rotate aroundthe axis. The differential rotation between the plates and the wave disccan be used as a rotary actuator or motor. As the force compressing theflex wave is increased the flex wave flattens, so the developed lengthof the outer portion of the wave disc gets closer in value to thedeveloped length of the corresponding contact region on the plates,resulting in an increased gear ratio. This increase continues until,with the wave disc flattened, the gear ratio becomes infinite. Thus thegear ratio can be varied by changing the distance between the plates.

In an alternative embodiment, the surfaces of the wave disc and theplates have lobes orientated essentially radially to provide positiveengagement. The lobes of the wave disc may be extended in the axialdirection to enable the transition from curved to flat shape of the wavedisc to splay the lobes prior to engagement with the lobes of the plateas a result of the smaller circumferential radius of curvature prior tothe wave disk flattening against the output member/s.

In an alternative embodiment, the surfaces of the wave disc and theplates have V shaped ribs orientated circumferentially to provideincreased friction and a self-centering action of the wave disk with theoutput members. The distance between the peaks of the ribs of the wavedisc reduces during the transition from curved to flat shape as the wavedisc engages with the plate to increase friction and increases duringthe transition from flat to curved as the wave disc disengages from theplate.

In an alternative embodiment, there are two or more wave disc and platesets with the wave disc ID's connected to increase the torque capacity.

In an alternative embodiment, there are two or more wave disc and platesets with the ID of the wave disc connected to the plates of the nextwave disc and plate set to increase the overall reduction ratio.

In an alternative embodiment, the plates are not constrained to rotatetogether. The plates are positioned to not be symmetric about the centerof the wave disc. The asymmetry of the plates generates differentialrotation between them. The rotation of the wave disc can be used just togenerate differential rotation between the two plates or it can be usedto generate rotation at a secondary speed. Differential rotation of thetwo output members in this way, is expected to provide extremely highreduction ratios.

In an alternative embodiment, electromagnets mounted on carrier platesthat are connected to the inner portion of the wave disc sequentiallyattract and repel, in an axial direction, pieces of steel mounted aroundthe wave disc to force the deformation to rotate around the axis.

In an alternative embodiment, electromagnets mounted on carrier platesthat are connected to the inner portion of the wave disc sequentiallyattract and repel, in a radial direction, pieces of steel mounted aroundthe wave disc to force the deformation to rotate around the axis.

In an alternative embodiment, electromagnets mounted on carrier platesthat are connected to the inner portion of the wave disc sequentiallyattract and repel, in a radial direction, permanent magnets mountedaround the wave disc to force the deformation to rotate around the axis.

In an alternative embodiment, electromagnets mounted on carrier platesthat are connected to the inner portion of the wave disc sequentiallyattract and repel, in a circumferential direction, pieces of steelmounted around the wave disc to force the deformation to rotate aroundthe axis.

In an alternative embodiment, electromagnets mounted on carrier platesthat are connected to the inner portion of the wave disc sequentiallyattract and repel, in a circumferential direction, permanent magnetsmounted around the wave disc to force the deformation to rotate aroundthe axis.

In an alternative embodiment, the shape of the wave disc is generated bymechanically expanding material at the outer region of the wave disc ina circumferential direction whilst leaving the material closer to thecenterline substantially unchanged. Electromagnets or other actuatorscan act from one area of the wave disk to another area of the wave diskto cause bending of local areas to propagate wave motion. This bendingdisplacement can be radial or circumferential or in between, as long asthis area would natural bend during wave propagation.

In an alternative embodiment, the shape of the wave disc is generated bymechanically contracting material at the inner region of the wave discin a circumferential direction whilst leaving the material at the outerregion substantially unchanged.

In an alternative embodiment, the wave disc is based upon a conicalprofile.

In an alternative embodiment, only one plate is used.

An embodiment of a wave disk has an ID 30 and an OD 32 and the ID is incircumferential compression and the disk material outward from the ID,here comprising spokes 34, is axially flexible enough to allow the ID tobuckle from its circumferential compression loading into anaxial/circumferential wave shape. The wave shape is then constrainedbetween one or more contacting rings that are fixed to the outputmember.

The embodiment may be modified according to any of the variationsdescribed in this disclosure as applied to the buckled OD diskconfigurations.

The schematic illustration of FIGS. 11-14 show the creation of thecircumferential wave shape according to one exemplary variation of thepresent device.

Many of the variations of the present device that are described herehave features that can be applied to other embodiments with differentfeatures. This disclosure describes examples of the variety of featuresof the present device in a variety of embodiments and variations thatmay be combined.

Other variations to this device are possible and conceived by theinventor. This disclosure is intended as an overview of the basicworking principles and does not describe in detail all the ways thesebasic principles can be combined or configured.

An example of a variation not illustrated here is a multiple diskconfiguration where more than one disk are arranged as an axial array.The disks can be in parallel to increase torque or they can be in seriesto increase reduction ratio.

The size of the devices illustrated here are in the 3″ to 10″ range butmuch smaller devices and much larger devices are envisioned by theinventor. Micro machine (MEMS) actuators can be constructed according tothe principles of this device using silicone and other materials thatcan be formed by forging or by CTE differentials etc.

Very large actuators of one to ten meters in diameter or largeraccording to the present disclosure are envisioned for large scaleapplications such as, but not limited to telescope rotation stages orlarge machinery requiring rotary motion. In these cases, combining thefeatures of certain embodiments such as a very high number of waves witha circumferentially grooved interface between the wave ring and theoutput members can allow a very large diameter with no additionalcentering bearings and a very large ID opening.

A circumferentially uninterrupted ring resists compression in thecircumferential direction. The OD ring 32, in this schematic of FIGS.11-14, represents an actual ring or simply the OD section of the disk.Compression loading of the ring in the circumferential direction can beaccomplished a number of different ways. In this case, radially inwardforce is applied to the OD ring by reducing the length of the generallyradial spokes 34. The spokes can radiate from a centrally located point(in which case they would be truly radially aligned. It is beneficial inmany applications to provide a center though hole in the actuator so anID ring is shown. The ID ring can be rigid or flexible in the axialdirection but is preferably rigid to allow attachment of a referencemember such as, but not limited to a robotic base.

When the radial length of the spokes is shortened, the OD disk finds alower energy shape as something similar to a hyperbolic paraboloid, asshown in FIG. 14.

The spokes 34 in this schematic are preferably linked to the rings witha low friction ball joint. Non-limiting examples of other spokeconstructions include cables or strings or wires or flexures whichcreate radial tension inward on the OD ring and which allow axialmovement of the ring so the wave can be propagated.

In another non-limiting example of the present device, as shown in acircular and rotationally symmetric disk of material is manufactured forexample by molding or turning on a lathe or casting etc. from a flexiblematerial such as, but not limited to metal or plastic or a composite orceramic. Metal materials are considered to be well suited for thisdevice because they exhibit adequate flexibility and strength in bothcompression and tension and does not creep or cold flow. Creep and coldflow are detrimental characteristics in this application because thedisk is preloaded and a material which cold flows will be more prone tobias toward a wave position if it is left at that position for anextended period of time. Plastic is generally less expensive and lighterthan steel but is more prone to cold flow (creep) and hysteresis losses.Nitinol is useful here because of its very high fatigue life and highelongation limit.

The disk is then pressed or forged between two mandrels 36 (section viewshown in FIG. 15) that are shaped to cause sufficient interference with,and thus to exert enough force on, the OD ring 38 to deform the OD ring(and preferably the outermost section of the disk 40 inward of the ODring but progressively less axial compression and plastic deformation ofthe disk 40 toward the ID hub area 42.) The component of this is plasticdeformation which elongates the OD ring 38 in the circumferentialdirection which results in a radial tensioning of the disk section 40inward of the OD ring. When the mandrel is removed, the disk willnaturally buckle around the OD in the circumferential directionresulting in a shape similar to a hyperbolic paraboloid with twopositive wave apexes and two negative wave apexes as shown in otherexamples in this disclosure.

By applying an axial load to the disk from preferably, but notnecessarily, both axial sides of the disk, and preferably to just the ODring area with a circular surface such as but not limited to a planarsurface, the circumferential wave will compress axially and provide apreloaded traction or geared or lobed interface at two contact zones onone side of the disk and two contact zones on the other (geared or lobedinterface may or may not be preloaded). If this axial preload isincreased to beyond the load carrying capacity of the two wave shape,the disk will naturally find a lower energy shape which is more able tosupport the increased load as a three wave OD ring shape as shownschematically in FIG. 17.

If this axial preload is increased to beyond the load carrying capacityof the three wave shape, the disk will naturally find a lower energyshape which is more able to support the increased axial load as a fourwave OD ring shape as shown here schematically (without the preloadingoutput ring members). Note that the radial lines on these schematic diskimages are only to indicate the apex position of the waves. The disk ispreferably made of one piece of material with no seems or joints. Cutouts or spokes may be beneficial in some applications, but the OD ringpreferably has at least one reasonably uninterrupted ring around it'scircumference to provide adequate circumferential compressive strength,stiffness, and smooth interaction with output disks during wavepropagation.

As the axial loading of the disk is increased (axial load preferablyprovided by an output contact ring (only shown in some of these images)it will produce increased axial displacement of the output rings andincreased axial compression of the wave shape and the disk will continueto increase the number of waves.

FIGS. 18-25 are a non-limiting example of increased wave numbers, from 4to 11 consecutively, that will occur as preload is increased. Theexamples show up to an 11 wave disk shape but larger number of waves arepossible and may be beneficial in certain applications where greaterload carrying capability and/or reduction ratio are required and/or verylarge diameter actuators of the present device. The larger the number ofwaves, the smaller the individual wave, and the OD disk may need to beaxially thinner to allow the smaller waves to form as the number ofwaves increases. For example, it may be that the disk shown may not besufficiently thin to reach the number of waves shown in the figures, andmay stop increasing in number of waves at, for example, six or sevenwaves due to misalignment or variations in manufacturing tolerances.

FIG. 25 shows the disk with eleven waves and with the axial load membersconstraining the disk. The axial load members are preferably shaped toallow unimpeded rolling wave contact propagation with minimal sliding.This allows the axial load members to act as output members to provideoutput rotation and torque for a variety of applications. The axial loadmembers would typically act as output rings and be fixed to a housingmember (not shown). FIG. 26 shows a section view of FIG. 25.

In the exemplary embodiment of FIGS. 27-30, the inner disk area hascut-outs 44 that allow the inner disk area to be more flexible. Thisreduces the forces on the OD ring that would prevent it from buckling. Alimitation of the cut-outs is the reduction of toque transfer capabilitythough the spokes to the ID hub, so this must be designed with themaximum torque requirement in mind.

The example in FIGS. 27-30 is shown as a two wave disk shape, but it canalso be preloaded into a shape with a greater number of waves.

An exemplary method of propagating the wave form is shown in FIGS.31-35. An array of electro-reactive strips 46 such as but not limited topiezo ceramics are fixed to one or both side of a disk. These may be inany orientation or angle and may be of virtually any shape as long asthey can be energized in such a way as to impart a force on the wavedisk that would cause it to propagate the wave to exert torque on theoutput members. In this non-limited example, piezo ceramic strips areadhered to the spoke blades 48 on both sides of the disk. The piezostrips are energized alternately from one side to the other to impartlocal radial bending moments on the disk. The piezo strips arepreferably wire connected near the ID hub where the movement is minimalto reduce fatigue stress on the wire and connections.

The piezo (or other active material) strips or patches (or areas if theentire surface is covered with a piezo coating or disk) are commutatedin a way that exerts a similar axial force on all of the waves at thesame time. This force may not be very large (e.g., 0.5 newtons per stripon an 8″ diameter disk) but the very high reduction ratios that arepossible with this device and the low friction that is possible form apure rolling contact between the disk and output members allows a highnumber of piezo strips to actuate at high frequency to produce a largeamount of input power per revolution of the output members. Wireconnections 50 connect the piezo strips to a power source.

The commutation of the piezo strips can be done a number of differentways such as but not limited to overlapping +− voltage sine wave formsas shown in FIG. 33. FIG. 33 is a graph showing applied voltage versustime for the different poles indicated by reference numerals 52A-52I.Each sine wave shown could also be a non-sine-wave shape, but simplesine waves are shown for simplicity. The commutation strategyrepresented by FIG. 33, while shown for piezo control, could be used formagnetic control or many other types of actuation means. FIG. 34 showsthe position of poles 52A-52I on the wave disk in this example, at thepoint in time marked by the vertical dashed line in FIG. 33.

Each curve in FIG. 33 could represent the driving current (if, for anon-limiting example, the controller is driving an electromagnet arraywhich is attracting and repelling an array of permanent magnets attachedto the wave disk). If driving a piezo ceramic array on a wave disk, thewaves shown in FIG. 33 could represent the voltage applied to each pole.A pole can consist of more than one magnet or piezo or other type ofactuation means. The non-limiting example of FIG. 33 has nine polescorresponding with 18 piezo strips on both sides (total of 36 strips perdisk) of a wave disk that is axially constrained to produce a three waveshape. With piezo strips on both sides of a three wave disk, one polewill preferably drive three equally spaced strips (at 120 degreeincrements) at the same polarity on one side of the disk, and for wiringsimplicity, three piezo strips directly opposite (axially aligned) inwhatever polarity necessary to produce the opposite axial deflection.Thus, both piezos in each pair of piezos have a radial section of thedisk sandwiched between them and work to deform the disk in the samedirection when energized with either a positive and negative polarityrespectively. The first pole, indicated by reference numeral 52A in thisexample, would be at max positive voltage while the sixth pole,indicated by reference numeral 52F, would be at max negative voltage andpole 8, represented by 52H, would be at zero voltage at a wave apex andso on.

It should be noted that these same (or separate) piezo actuators (orother sensors such as strain gauges) attached to the disk can be used assensors to provide the controller with information about the shape ofthe wave disk and the position of the waves. This data can be used, forexample, as a wave disk encoder by sensing wave propagation angle, or tosense torque on the actuator (based on the asymmetrical deformation ofthe wave form).

It should be noted that many other control strategies or numbers ofpoles are anticipated by the inventor. This is only given as anon-limiting example of how the wave disk wave propagation can beaccomplished and controlled.

The controller could be in many different configurations but couldcomprise, for example, a CPU that provides a variable voltage to anarray of poles based on a programmed torque and/or motion requirementand feedback information from position sensors in the actuator.

FIG. 35 shows a simplified schematic of a non-limiting example of one ofmany ways the present device could be controlled to propagate the waveson the wave disk 1. A power supply 54 provides electrical power to theCPU/motor controller 56 which provides variable voltage to an array ofpiezo actuators 46 (only three shown here but any number could be used).The position of the waves and the torque on the wave disk can be sensedby one or more strain gauges 58 or other sensors (including, possibly,the use of the piezo or other type of actuators, which may be capable ofsending a feedback signal to sense their deflection).

If a traction drive torque transfer is used with this device, it ispreferable to have an encoder between the input and the output. Thisencoder can be relatively low resolution if the preload of the tractionsurfaces is adequate to provide predictable motion transfer over a rangeof speeds and torques and temperatures. To maximize the precision andthe accuracy of the output based on a digital output encoder, for anon-limiting example, the high resolution feedback from one or morestrain gauges on the wave disk would provide resolver-type of feedbackto the motor controller. This feedback will tend to be very sensitivewith regard to changes in wave disk shape but it will drift relative tothe output rotation due to slippage between the wave disk and the outputraces. Due to the repeatable nature of this device, this slippage % canbe measured empirically under a range of operating conditions and usedto predict the amount of slippage between the wave disk and the outputrings under various conditions as sensed by sensors on the disk and inthe actuator.

Using a combination of sensors in this or a similar way will allow veryprecise control by monitoring the strain gauge or piezo (or otherproportional sensors) and by resetting or recalibrating the position atevery digital pulse feedback signal from the lower resolution outputencoder.

An example of a low cost embodiment is shown in FIG. 36. It uses aninjection molded disk 60 which is preferably made of a material that hasa high shrinkage % when demolded. And array of more rigid (incompression) inserts 62 are molded into the ring during injectionmolding. These plugs can be of any material including permanent magnetmaterial.

When demolded (preferably after the part has cooled to room temperaturein the mold) the contraction of the disk material will cause thecircumferentially more rigid (in compression) OD ring to bucklecircumferentially. FIG. 37 shows a close-up view of the imbedded insertswith hidden lines made visible.

If permanent magnets are used for the inserts, they can possibly bemagnetized after demolding to make assembly easier. The inserts can becontacting or not contacting depending on the various materialproperties. The inserts may also be a single piece of material such as aring 64 of steel or titanium etc. as shown in FIG. 38 and in closeup inFIG. 39. The insert ring 64 is stiffer in compression circumferentiallyand has a lower coefficient of thermal expansion (CTE) so when the diskcools after injection molding at high temperature, the surroundingplastic contracts and causes the inserted disk, which may be made ofspring steel, for example, will buckle circumferentially to create thewave form.

A non-limiting example of an asymmetrical embodiment of the presentdevice is shown in FIG. 40, with a close-up view in FIG. 41.

In this embodiment the torque transfer from reference member 70 tooutput member 72 is from one housing side to the other, instead of fromthe wave disk to a housing member. The wave disk is still transferringthe torque from the reference member contact surface to the outputmember contact surface, but it is not rigidly attached to either.

With this embodiment, one of the contact surfaces 74A is constructed toallow greater circumferential length change for a given bend radius ascompared to the other contact surface 74B. This differentialcircumference length change can be accomplished in a number of ways.Non-limiting examples include non-circumferential grooves that aredeeper in one surface than the other so to allow the segments betweenthe grooves to expand circumferentially more on one side compared to theother. Longer teeth or lobes on one surface can have a similar effect.The position of the inner disk relative to the two axial surfaces willaffect the contact surface expansion as well. The surfaces may betraction surfaces or toothed or lobed surfaces. In any case, thedifference in the amount of circumferential surface elongation from thecontact surface on one side of the disk to the contact surface on theother side of the disk is believed to result in a differential rotationbetween the reference and output contact surfaces when the wave diskwave is propagated. This differential rotation can be very smallallowing for very high reduction ratios and high precision control ofthe output angle.

Ratios of 1000:1 or more are believed possible in some configurations.

A thrust bearing 76 is provided between the two housing members 78A and78B to allow the relative rotation. The wave propagation means is notshown but can be any type disclosed here or other types not disclosed.

A variation of the differential wave disk of FIGS. 40-41 is shown inFIG. 42 with slots 80 in the greater offset side of the OD ring. Theslots can be of any shape including but not limited to radial or spiralas shown here. The purpose of the slots is not to create positiveengagement like gear teeth, but to allow greater circumferentialexpansion of the slotted surface as compared to the non-slotted surface.The effect is believed to be a greater effective length change of theslotted surface as compared to the non-slotted surface for a greaterdifferential effect between the reference race and the output race.

Slots of different depths may be used on both sides. Slots may be on oneside or both sides and the disk may be symmetrical or non-symmetrical.The disk may be used, as shown in FIG. 43, in a device otherwise thesame as that shown in FIGS. 40-41.

FIGS. 44-46 are some additional simplified partially assembled images ofa lobed configuration showing how the wave disk OD ring 82 with lobesskips one or more lobes on the output circular lobe rings 84 with everywave. The disk shown here has symmetrical lobes on both axial contactsurfaces but according to the principles of this device as disclosedhere, the number of lobes on the two wave disk contacting faces could bea different number and/or they could be different lengths.

Additional Variations

One or more permanent or electromagnets can be attached to a spinningmember that is coaxial to the wave disk. The magnets will attract thewave peaks of the disk and cause them to propagate when the magnet diskis rotated. The waves can also be propagated with a contacting rollerbearing or bushing. The wave disk waves can be propagated with anoncontacting bearing such as an air bearing or a fluid dynamic bearing.The wave disk waves can be propagated using hydraulic pressure and/orfluid dynamic forces such as with compressible or incompressible fluidinertia or Coand{hacek over (a)} effects. High elasticity materials withhigh cycle life may be used such as, but not limited to, Nitinol metal.Nitinol is a nickel titanium alloy, for example in approximately equalatomic percentages. Nitinol or other memory or heat reactive materialscan be used to provide very high forces for some applications. Thismaterial can be used in a similar way to the piezo actuators describedhere, or the nitinol can be used as wire spokes that are tensioned likebike spokes to achieve the initial preload and wave shape. Once the waveshape is set, the wires can be heated and cooled to propagate the wave.This may be useful for very large applications where high forces areneeded but high speed is not important.

FIG. 47 shows a non-limiting example of an embodiment with permanentmagnets 86 on one or both axial sides of the disk and an array ofelectromagnetic coils 88 attached to the disk, for example with aflexible ring. This would operate more like an audio speaker with amoving coil with the advantage of potentially lower inertia and fasterresponse time. The permanent magnets may be, for example stationary andfixed to the reference member and/or output member, or they may beattached to the disk hub member.

Many of the variations of the present device that are described herehave features that can be applied to other embodiments with differentfeatures. This disclosure described examples of the variety of featuresof the present device in a variety of embodiments and variations sosomeone skilled in the art can combine the various features withdifferent effects.

Other variations to this device are possible and conceived by theinventor. This disclosure is intended as an overview of the basicworking principles and does not describe in detail all the ways thesebasic principles can be combined or configured.

An example of a variation not illustrated here is a multiple diskconfiguration where more than one disk are arranged as an axial array.The disks can be in parallel to increase torque or they can be in seriesto increase reduction ratio.

Many of the same principles described here in relation to wave disks mayalso be applied to linear actuators or semi spherical actuators.

They may also be applied to a ring actuator with an ID ring that isforged or formed according to the principles of this disclosure with thedifference of the radial disk member being in compression loading so asto cause the expanded ID ring to buckle circumferentially. The wave canthen be propagated according to any of the methods described for the ODbuckled wave disk.

FIGS. 48 and 49 show a non-limiting simplified partial assembly exampleof a three wave circumferentially buckled ID ring disk. The disk 90 isbuckled on inner diameter 92 and connects to output races on innerhousing 94.

FIG. 10 shows a cross section view of a wave disk with two housingcontact races that use a circumferentially revolved ridge shape 26 onthe disk and matching groove shapes 28 on the housing/output contactsurfaces. The purpose of the grooves and ridges is to increase thecontact pressure between the disk OD ring contact surface and the outputring contact surface/s through a wedging effect. The disk in thissection is shown half way between the two contacts.

It is believed that a high angle will increase the tractive forcedramatically and that a locking taper angle may even be beneficial andmay work without undue friction due to the radial contracting of theridges on the disk as they experience the smallest radius wave curvaturejust before coming into contact with the output contact grooves. This isexpected to expand the ridges radially into the groves after contact hasbeen made and before unwanted sliding can occur. When the disk bendsagain when the contact becomes non-contacting, the radial thickness ofthe ridges will again contract due to circumferential bending of theridges, to unseat them from the locking taper engagement.

Shown in FIG. 50 is a simplified schematic view of a linear actuator 96using the principles of the present disclosure. There are no bearingsshown. The outer edges of the flex plate 98 are expanded in the lineardirection compared to the centerline 100 which is attached to a fixed orreference member. The two housing members 102 are the output members.The waves can be propagated in the same way that the disk waves can bepropagated with magnets or piezos etc. The flex plate alone is shown inFIG. 51.

To exert greater force on the disk with piezo or other active materialor other actuation means such as, but not limited to hydraulics or gaspressure, a piezo stack can be placed at a location where thelengthening of a stack will result in an axial movement of the OD ring,as shown in FIG. 52. An opposing stack can be used to provide force inthe other direction. Only one set of opposing piezo stacks is shown inthis example but an array of piezo stacks (or other actuator means) ispreferred. Piezo stack actuators are shown as an example here but anykind of actuator that exerts a linear force can be used in a somewhatradial force angle alignment similar to that shown here. FIG. 53 shows acutaway view of the piezo stacks, showing more clearly the opposingstacks 104A and 104B. The piezo stacks preferably have convex curvedends to allow angle change with no sliding. The ends 106 of the piezostacks are preferably semi-spherical, or at least are rigidly orflexibly attached to the disk via concave curvature receiver membersreceiving convex curvature ends of piezo stacks. An advantage of thisconfiguration of FIGS. 52 and 53 is the elimination of bendingdisplacement on the piezos, as with the bonded piezo stripconfigurations. This allows much thicker and more powerful piezoactuators that act on the disk by exerting a radial or near-radial forceslightly off-center so as to induce axial force on the disk

FIG. 54 shows a sectional simplified schematic of a non-limiting exampleof how one or more actuators 108 of any radially or generally radiallyexpanding type (such as, but not limited to piezo, or hydraulic or gaspressure or any type of electro-active or magnetostrictive or thermalexpanding or memory metal material can expand or contract to produce anaxial wave propagation effect. The angle of the offset is shown on theID end of the actuator here could also be on the OD end or both.

Additional Non-Limiting Examples of Linear Embodiments

FIG. 55 shows a simplified schematic non-limiting example of a linearwave plate (or foil) with electroactive wave propagating elementsadhered to the surfaces of the wave foils. The foils are arrayed to forma wave plate array 110 around a fixed core and an array of outputsurfaces 112 moves as the waves on the array of foils are propagated inunison. FIG. 56 shows an end view of the same design.

FIGS. 57-59 show a linear actuator according to the principles of thepresent device with the wave foils fixed to the outer member. There aremany ways to configure the various components of a linear embodimentthat are anticipated by the inventor. In this example, one or more wavefoils are attached to a movable outer member 114 with preferably two ormore wave foils situated at an angle to each other (90 degrees is themost effective but other angles can work with different effects) tocenter the fixed/reference center spar 116 in two planes (each planebeing perpendicular to the lengthwise direction of a wave foil).

FIGS. 60 and 61 show a partial view of a simplified schematic of a wavefoil embodiment according to the present disclosure. Slots 118 areprovided between the active material bending actuators 120 to allow wavecreation (according to one or more of the various wave creationstructures and methods in this disclosure) with reduced lengthwisebending of the plate where the actuators are attached. In embodimentsthat use piezo (or other active material) to propagate the wave/s, theactuator is more suited for lengthwise (lengthwise for the actuator, notthe plate, in this example) bending than sideways bending. Slots in thefoil, similar to those shown here, reduce this sideways bending of theactuators.

Non-Limiting Examples of Semi-Circular Actuators

One or more features of the present device as disclosed here can beapplied to a semi-circular device which actuates over a limited angulardistance. Here, “semi-circular” is taken not to be restricted to a halfcircle but to refer to any fraction of a circle. An advantage of such asystem is the ability to semi-encircle a structure or body and apply atorque to it. Non-limiting examples include but are not limited to useon an exoskeleton where a semi-circular actuator can semi-encircle theuser's joint (such as, but not limited to, a shoulder joint where theactuator can share the same pivot location as the user's shoulder joint.Another example would be a powered open-end ratcheting wrench that onlyneeds 40-70 degrees of rotation to provide the necessary movement.

FIG. 62A and FIG. 62B are a top and end view respectively of theunstressed foil shape before creating the wave shape. Note that theseare not partial sections of the arc foil. The arc can be of any angle. A90 degree foil is shown here as an example of a partial disk foilconfiguration. Also, the wave can be on the ID and/or the OD of thesemi-circular wave foil.

The wave is created by slightly straightening the non-wave edge of thefoil, as shown in FIG. 63 and FIG. 64 with the wave-formed foil 124superimposed above the at-rest foil 122.

FIG. 65 shows a simplified incomplete assembly of the abovesemi-circular wave foil sandwiched between two output surfaces 126.Output surfaces are also preferably an arc shape and can be a completecircle or a semi-circle as shown here.

In the exemplary embodiment shown in FIG. 66, a curved semi-circularwave foil is planar when at rest and then curved in two planes.Straightening it slightly creates the initial wave-form. Curving it at90 degrees to the first plane (or other angles can work) allows the waveto propagate between to concentric surfaces (cylindrical here, but canalso be conical). Shown here is the at-rest foil 122 on the right whichis planar with a slight curvature (and a preferably thicker sectionwhere it will be fixed when pre-loaded). On the left is the same foil124 after straitening in direction 1 and bending in an arc in direction2. The concentric output surfaces are preferably connected to each otherand will rotate around the common arc center when the wave is propagatedby means described in this disclosure for other wave member embodiments.

It should be noted that one or more of the features and methods whichare described for the disk embodiments of the wave disk actuator canapply to the wave foils embodiments. These include but are not limitedto:

Wave propagation by electromagnet commutation; and

Wave propagation by active materials such as, but not limited to,electroreactive materials.

Construction techniques which include but are not limited to molding ofa material which shrinks when cooled with one or more inserts of amaterial along the wave edge that has a lower coefficient of thermalexpansion.

Commutation of an electromagnet array, for example on or attached to oneor both planar surface members, can be used to attract and/or repel thewave disk and/or magnets and/or soft magnetic portions of or inserts onthe wave disk axially to hold or move the apex of one or more waves. Ifa geared interface is used, a wave apex will move promotionally to therotation angle of the wave disk to a planar surface member. If thecontact between the wave and the planar surface is a friction ortraction interface, the wave propagation angle and wave disk rotationrelative to a planar surface member will be variable. In both cases,sensors can be used to determine the angular position of a wave apex andthe electromagnets. An axial force on the wave disk ahead of a wave apexwill pull the wave apex in that direction. A repelling force on the wavedisk behind of a wave apex will commutate the wave in the same directionas an attracting force ahead of the wave.

A non-limiting exemplary embodiment of a wave disk 128 according to thepresent disclosure is shown in FIG. 67 with a preferred construction. Ituses piezo or other bimorph actuators 130 adhered to preferably bothside of the inner disk area. Radial cut-outs 132 are arranged such thatcircumferential flexibility of the inner wave disk area is increased. Anarray of bimorph actuators are attached to the wave disk surface/s sothat radial contraction of an actuator causes deformation of the diskaxially toward that actuator. In order to reduce the circumferentialdeformation and stress on an actuator, a radial cutout 134 in the innerdisk area is located within the circumferential width of an actuator forall or preferably at least the outward end of an actuator. This allowsthe outermost ends of the spokes to which said actuator is attached to,to act as a flexure to reduce the circumferential deformation of theinner wave disk from causing as much circumferential deformation andstress on said actuator during wave propagation. FIG. 68 shows a detailview of a radial cutout 134 located within the circumferential width ofan actuator.

FIG. 69 shows a simplified partial assembly of an exemplary embodimentof a rotating input configuration for a wave disk. It has a rotatingmember 136 that houses permanent magnets 138 that rotate with it andpull a wave along.

FIG. 70 shows ahere is an example of a spinning input member with acontacting rolling wave propagation member. Wheel 140 in rotating member136 contacts the wave disk to propagate the wave.

Axial Lobes

FIGS. 71 and 72 show a detailed view of a partial assembly of anon-limiting exemplary embodiment of an axially lobed wave disk 142.Both output rings 144 in this example are at a fixed axial distance fromeach other and connected for simultaneous rotation around the actuatorcenter axis. The output members are preferably axially preloaded towardeach other with the wave disk sandwiched between them. This conforms thewave disk lobe tips to the planar (or conical) lobe roots on the outputrings for preferably three or more lobe tips per engagement (althoughmore or less than three teeth may have benefit under some conditions).

The benefit of three or more lobe tips in engagement is a smoothertransfer of each lobe tip from non-contacting to contacting as the diskaxially “flattens” against the output rings.

Another beneficial effect of this flattening is the increased elasticdeformation of the disk just before contact (at a smaller radius ofcurvature circumferential wave section). This has the effect of splayingthe lobe tips to increase the circumferential distance between the disklobe tips just before engagement. The lobes are longer in the axialdirection than a conventional involute tooth profile would be. The exactlength needs to be determined by analysis and/or testing for eachapplication, but the inventor has found that an aspect ratio of lobeaxial length to width of somewhere between 2:1 and 6:1 can provide thedesired results, although aspect ratios smaller or greater may also workin certain applications.

The result of the elongated lobes and lobe tip splaying is a delaying ofthe disk lobe tip contact with the output ring lobe roots until the disklobe tips are closer to the bottom of the output ring lobe roots. Thebenefit of this is reduced sliding of the disk lobe tips and the outputring lobe roots. Less sliding results in reduced friction, reduced wear,and the possibility of operation without lubrication in certainapplications.

As shown in FIG. 71, the contact area (as indicated by reference numeral146) of the disk conforms to the output ring because of axial preload ofthe ring on the disk. The smallest/tightest curvature of the disk due toaxial displacement happens just before engagement of disk with ring, asindicated by reference numeral 148. This causes axially elongated disklobes to splay circumferentially, delaying contact of disk lobe tipswith ring lobe roots until disk lobe tips are more fully engaged in ringlobe roots.

FIG. 72 is a detail view of the embodiment of FIG. 71 showing playing oflobe tips to prevent disk lobe tip contact with ring lobe until disklobe tips are preferably at ring lobe roots. As shown in FIG. 72, disklobes are axially elongated to produce a splaying effect in thecircumferential direction, indicated by the arrow marked with referencenumber 150, as the wave is propagated. This splaying effect is greatestas the tightest curvature just before disk lobe contact with ring loberoots. The result is a delay of contact at the locations marked byreference numeral 152 until the disk conforms to the ring in the contactzone where curvature is reduced and lobe tips transmit torque withreduced sliding at locations marked by reference numeral 154. Lobes arepreferably not contacting at locations marked with reference number 156.Lobes on one output member may be longer (h1) than the lobes on theopposed output member (h2), for example by 10%. The teeth or lobes onone axial side of the wave disk may be axially longer than the teeth onthe other axial side of the wave disk as shown in FIG. 71. The longerteeth may be of the same number as the other teeth but of a differentcircumferential pitch, or they may be of the same circumferential pitchas the other teeth but of a different number. Other variations of toothpitches and numbers are possible, the objective for a differentialoutput configuration being that the ratio of movement between the wavedisk and one output member is slightly different than the ratio ofmovement between the wave disk and the other output member during wavepropagation.

The disk may be made of a metallic material such as nitinol with anon-metal contact surface such as a polymer on one or more of thecontact surfaces between the disk and output or reference members. Thisprovides for reduced noise and/or increased traction. For example,aluminum on nylon is a unique combination that can provide high frictionwithout galling the aluminum. Many other combinations of materials canbe used. A high durometer urethane is another material that can providehigh traction, resilience and low hysteresis for low rolling resistance.If a resilient material is used, the wave disk contact surface can havea non-smooth finish to increase traction.

The disk may be made of an injection molded part of a material having afirst coefficient of thermal expansion (CTE) but with an imbedded ringnear the OD of the disk with a lower coefficient of thermal expansion(CTE). As the injection molded disk cools (preferably in the mold), theradially inward tension created as the injection molded material coolswill create a circumferential compression load on the lower CTE ringwhich is sufficient at the operating temperature of the actuator tocause and maintain a circumferentially buckled waveform.

In a method of manufacturing, the creation of waves in the disk may bedone by greater axial plastic compressive deformation of the outer ring.This circumferentially elongates the outer ring to the point of causingit to circumferentially buckle. Axial plastic compression deformation ofthe entire outer ring can be done at once with a single or multiplecompression procedures (such as forging), or it can be done by rollforming the outer ring with one or more sets of rollers whichprogressively circumferentially lengthen the outer wave ring. The discmay also be made by roll forming.

Referring to FIGS. 73-75, a method of manufacture of a wave actuator isshown. A disk 160 is provided with a circumference, the disk being in aninitial state, typically flat. The disk is loaded in tension across thedisk and compression along the circumference to cause the disk to buckleand form a wave shape with waves, as shown in FIG. 74. The disk 160 isconstrained between output members 162, 164 with the output memberscontacting the disk at one or more wave apexes such that force can betransferred from the disk to the output members when a wave ispropagated along the disk. The output members exert enough force on thedisk member to increase the number of waves from its the initial statewhen the wave circumference is loaded in compression and beforecontacting the output members. The disk and output members may beprovided with teeth and meshing respective teeth of the disk and outputmembers. Loading the disk in tension across the disk and compressionalong the circumference may comprise providing the disk with a ring 166,and the disk 160 and ring 166 being made of materials of differentcoefficients of thermal expansion, and subjecting the disk to atemperature set to cause the disk and ring to expand or contractdifferentially.

FIG. 76 shows a schematic of a roll forming manufacturing method. Arotationally symmetrical disk 170 is fabricated and then spun around itsaxis while increasing axial force is applied through the rollers 172.The contact force of the rollers 172 is sufficient to exceed the plasticdeformation limit of the ring. This circumferentially lengthens the ringto the point where the lowest energy state is a circumferentiallybuckled wave.

In the claims, the word “comprising” is used in its inclusive sense anddoes not exclude other elements being present. The indefinite articles“a” and “an” before a claim feature do not exclude more than one of thefeature being present. Each one of the individual features describedhere may be used in one or more embodiments and is not, by virtue onlyof being described here, to be construed as essential to all embodimentsas defined by the claims.

What is claimed is:
 1. A wave actuator comprising: a two dimensionalstructure having at least a portion pre-stressed in compression in afirst direction of the two dimensional structure to form a wave shapehaving waves along the first direction; an output arranged in contactwith the waves of the wave shape, the output and the two-dimensionalstructure movably arranged in relation to one another; and a wavepropagator arranged to propagate the waves along the first direction tomove the output relative to the two dimensional structure, in which: theoutput is in geared contact with the waves of the wave shape; the twodimensional structure has axially elongated teeth on each side of thetwo dimensional structure, the axially elongated teeth splaying inoperation to create increased tooth tip pitch before contact with theoutput; and the axially elongated teeth on one side of thetwo-dimensional structure are longer in a direction generallyperpendicular to the two-dimensional structure than the axiallyelongated teeth on the other side of the two-dimensional structure. 2.The wave actuator of claim 1 in which the output comprises a firstoutput member and a second output member, the wave shape beingconstrained between the first output member and the second outputmember.
 3. The wave actuator of claim 2 in which the first output memberis rigidly connected to the second output member.
 4. The wave actuatorof claim 2 in which the wave shape comprises a first contact surfacethat contacts the first output member and a second contact surface thatcontacts the second output member, one of the contact surfaces beingoffset in a direction generally perpendicular to the two-dimensionalstructure to cause the wave actuator to differentially move the firstoutput member and the second output member.
 5. The wave actuator ofclaim 4 further comprising a slot in the one of the contact surface thatis offset in the direction generally perpendicular to thetwo-dimensional structure.
 6. The wave actuator of claim 1 in which thewave propagator comprises piezo actuators attached to the twodimensional structure and aligned within the two dimensional structuregenerally perpendicular to the first direction.
 7. The wave actuator ofclaim 1 in which the wave propagator comprises electromagnets.
 8. Thewave actuator of claim 7 in which the electromagnets are configured toattract the two dimensional structure.
 9. The wave actuator of claim 7in which the electromagnets are configured to attract or repel permanentmagnets.
 10. The wave actuator of claim 9 in which the electromagnetsare mounted on the two dimensional structure.
 11. The wave actuator ofclaim 9 in which the permanent magnets are mounted on the twodimensional structure.
 12. The wave actuator of claim 1 in which theoutput is in friction contact with the waves of the wave shape.
 13. Thewave actuator of claim 1 further comprising a reference member, the waveshape being constrained between the output and the reference member. 14.The wave actuator of claim 2 in which the wave shape is compressedbetween the output members to create two or more contact patches on thefirst output member and an equal number of contact patches on the secondoutput member.
 15. The wave actuator of claim 14 in which the firstoutput member and the second output member compress the wave shape withsufficient contact pressure to create flattened portions of the twodimensional structure where the two dimensional structure contacts thefirst output member and the second output member.
 16. The wave actuatorof claim 1 further comprising grooves extending generally in the firstdirection in each of the disk and the output.
 17. The wave actuator ofclaim 16 in which the grooves have angled shapes to increase the contactpressure as a result of loading of the disk against the output.
 18. Thewave actuator of claim 1 in which the two dimensional structurecomprises a first material having a first coefficient of thermalexpansion, and a second material having a second coefficient of thermalexpansion, the first coefficient of thermal expansion being differentfrom the second coefficient of thermal expansion, the two dimensionalstructure being formed at a first temperature and used at a secondtemperature to pre-stress the two dimensional structure in use.
 19. Thewave actuator of claim 1 in which the two dimensional structure isarc-shaped.
 20. The wave actuator of claim 19 in which the pre-stressedportion is an edge portion at an outer edge of the arc, the edge portionpre-stressed in compression tangentially to the edge.
 21. A waveactuator comprising: a two dimensional structure having at least aportion pre-stressed in compression in a first direction of the twodimensional structure to form a wave shape having waves along the firstdirection; an output arranged in contact with the waves of the waveshape, the output and the two-dimensional structure movably arranged inrelation to one another; and a wave propagator arranged to propagate thewaves along the first direction to move the output relative to the twodimensional structure, in which: the two dimensional structure comprisesmetal, and the two dimensional structure contacts the output with apolymer to polymer interface.
 22. A wave actuator comprising: a twodimensional structure having at least a portion pre-stressed incompression in a first direction of the two dimensional structure toform a wave shape having waves along the first direction; an outputarranged in contact with the waves of the wave shape, the output and thetwo-dimensional structure movably arranged in relation to one another;and a wave propagator arranged to propagate the waves along the firstdirection to move the output relative to the two dimensional structure,in which the two dimensional structure comprises nitinol.
 23. A waveactuator comprising: a two dimensional structure having at least aportion pre-stressed in compression in a first direction of the twodimensional structure to form a wave shape having waves along the firstdirection; an output arranged in contact with the waves of the waveshape, the output and the two-dimensional structure movably arranged inrelation to one another; and a wave propagator arranged to propagate thewaves along the first direction to move the output relative to the twodimensional structure, in which: the two dimensional structure is abelt, the pre-stressed portion comprises an edge portion along an edgeof the belt, the edge portion being pre-stressed in compressiontangentially with respect to the edge, and the edge portion ispre-stressed in compression by a tension member applying a compressiveforce parallel to the edge to a portion of the belt parallel to butoffset from the edge.
 24. The wave actuator of claim 23 in which thebelt has a second edge substantially parallel to the edge and comprisesa second edge portion pre-stressed in compression tangentially withrespect to the second edge to form a second wave shape.